On that August 2009 night in Zurich, Switzerland, Dathan Ritzenhein immediately dropped to the back of the pack among the 15 runners in the 5000-meter race at the Weltklasse Golden League meet. Competing against the world's best, including world record holder Kenenisa Bekele, Ritzenhein came through the first lap dead last. Perfect, thought his coach, the legendary Alberto Salazar.

Before the race Salazar had told Ritzenhein, "Get to the back and go as slow as you can without losing contact." Doing just that, Ritzenhein remained calm, his pace steady at 61.8 seconds per lap. Eventually, a number of racers who had pushed the lead began to fall from the front and behind the American. With two laps to go, Ritzenhein had climbed to seventh place—even though his splits barely wavered by more than a second from lap to lap. At that point he finally sped up, pushing his previous pace by two seconds, and ended up in third place. His time of 12:56.27 sliced nearly two seconds off a 13-year-old American record.

But while his surge may have earned him a podium spot and a record, to this day Ritzenhein knows it was his adherence to his (and Salazar's) pacing plan that put him in a position for history.

"I fell into a groove," he says, "and it got easier as the race went on."

Whether you're a world-class runner like Ritzenhein or a weekend warrior who's just out there to finish a fast 10-K, finding the optimal pace can mean the difference between success and suffering. Determining such a pace would seem pretty straightforward. If you want to run a 3:40 marathon, say, it's a simple calculation to figure out that you need to run eight-minute, 23-second miles to meet your goal. But on the track, on the roads, and in real life, unexpected detours and surprises can shred your best pacing plan to pieces.

"We would like to be robots and turn the knob to our goal pace and just go, but we're human," says Greg McMillan, owner of the Flagstaff, Arizona-based McMillan Running Company who has coached elite national runners, including several Olympians. "When we encounter a slight hill or a slight turn, it makes a difference."

To run your best in your next race, consider the following questions, and then put their answers toward a new—and improved—pacing strategy.

What is the secret to pacing?A: Pacing isn't something most of us are born knowing how to do. Instead, like many skills, it takes practice. Why? So you learn what your goal pace feels like in your legs, in your gut, and in your head prior to race day. Deena Kastor, the American bronze medalist in the 2004 Olympic Marathon, puts it this way: "The best way to prepare for any distance is to find your rhythm in the months before the race."

The training paces in "Measuring Your Effort" (below) can provide the repetition needed to sustain your goal pace—and build confidence. Ritzenhein knows how critical the latter is. A few weeks before the world half-marathon championships in 2009, he ran a 10-mile time trial at his half-marathon goal pace. "The trial helped me get used to that pace so that it wouldn't feel so hard in the race," Ritzenhein says. The payoff: He took home a bronze medal.

Before your next race, McMillan suggests measuring a loop that's half to three-quarters the distance of your event and practice running it at your goal pace. (To determine that, try the calculator at runnersworld.com/pacecalculator.) "Run your loop and know how long it takes you," says McMillan. "Every other week, repeat this race-pace run at the same pace and notice how it feels." Over time, you'll learn how your breathing, heart rate, and overall effort feels at this level.

Can my race-day mental and physical states affect my pace?A: When you run, your brain receives dozens of physiological signals from the rest of your body—how hard your muscles are working, what temperature your body is, how fast your heart is beating. Your brain then processes the signals into sensations that you experience as perception of effort. But it's not just physiological signals that determine how hard your pace feels. "Expectation is just as crucial," says Ross Tucker, Ph.D., an exercise physiologist at the University of Cape Town in South Africa.

Here's what he means: If you're in the midst of a PR attempt, you'll expect to be working hard, and your brain will interpret the physiological signals and effort perception as signs that you're on pace. As a result, your effort level may feel quite manageable. But if you're out for an easy run and your training partner goads you into finishing at race-day pace, then you're likely to feel crummy. That's because, Tucker says, "your expectations and physiological feedback are so mismatched."

Set realistic expectations about how you'll feel during your race, erring toward discomfort. Then, to offset the expected pain, use positive stimuli—like family members cheering you at designated points along the course—to keep you on pace. Meghan Armstrong, a member of Team USA Minnesota, says, "I like to have my coach yell out each quarter mile to help me stay on the right pace."

Is being negative a positive?A: Coaches have long preached the virtues of so-called negative splits, where the second half of a race is run faster (and with speedier split times) than the first half. Apparently, those coaches knew why. Tucker recently analyzed world record performances from 1912 to 2004 and discovered that it's extremely rare for a record to be broken with a positive split. "Only in races of 800 meters or less," he says, "will you see the first half of the race" run faster than the second half. Otherwise, in longer distances, say, 5000 and 10,000 meters, "Nobody has ever broken a world record with a faster first half."

Okay, so negative splits seem to be the way to go, right? Not so fast. Instead of a pacing approach that relies on negative splits, coaches are increasingly leaning toward a so-called even pacing approach. Again, the data show why. "There was a time, until the 1980s, where the 5-K and 10-K records had a very fast start, slow in the middle, and fast at the end," Tucker says. Now, instead of holding back in the middle of the race and picking up the pace toward the end, today's top runners run an even pace throughout the whole race, Tucker says, with the only variation coming in the last kilometer or so when racers drop a final kick. "[Haile] Gebrselassie's current marathon world record [2:03:59] is relatively even-paced, and that's definitely optimal."

While a recent RW survey showed that a larger percentage of readers PR'ed with negative splits than with even splits, the pros recommend running an even pace the whole distance. "Negative splits [are] a skill that takes a long time to master and lots of training to get used to the amount of suffering you experience at the end of the race," says Matt Tegenkamp, the American record holder in the two-mile. "Even splits let you use the least amount of energy for the majority of the race."

How much will the right warmup keep me on goal pace?A: You can spend weeks training to prepare for your race-day pace. You can spend good money on gadgets that will keep you on track during a race (see "Going Steady," below). But if you don't spend a few minutes---a few quality minutes--warming up before a race at your target pace, then all that other work and expense may be lost. Amy Yoder Begley understands this. A 2008 Olympian, she says that before a race she'll run a few 200-meter intervals at race pace so she "knows what it feels like" before the competition begins.

The speed of your warmup should reflect your intended race pace and your race distance. If you're racing a 5-K, a relatively short distance compared to a half or full marathon, McMillan says your pace will be relatively fast. As such you'll need to rev up your muscles beforehand. Some short, fast intervals at just above race pace can prepare you to sustain that pace on the racecourse. On the other hand, if your finish time will be measured in hours, not minutes, skip those last-minute sprints; they could actually prime you to go out too fast. Instead, coach Jack Daniels, Ph.D., author of the classic guide, Daniels' Running Formula, recommends adding to your warmup a two-to three-minute run at your threshold pace (which is slightly slower than marathon pace). Daniels, who is the cross-country coach at Brevard College in Brevard, North Carolina, says that besides getting your body in tune with the effort it soon will put forth, such a warmup mimics the start of most runs. "In a series of interval runs in training, a runner's first interval is rarely the one that feels the best," he says. "Why not get rid of that first one before the race begins?"

It may sound counterintuitive, but in long-distance races, your warmup can actually be shorter and mellower than in speedier races. "If you have a tendency to go too fast in the marathon," McMillan says, "you might need to abbreviate your warmup and think of your first few miles as a part of your warmup."

Can I still salvage a race if I get off pace?A: Dave McGillivray has seen it happen all too often during his 10 years as race director of the Boston Marathon: An amped-up runner lets the early downhills of the famous course push her off the carefully planned pace strategy that she had spent months perfecting. "Correcting the mistake is simply a matter of self-discipline and backing off," says McGillivray. "But if you allow this to keep up for too long, you won't be able to reverse the negative effects." Like being fried by the time you hit Heartbreak Hill at mile 21.

You don't have to be caught up in the excitement (and hills) of Boston to get off track. Despite the best of intentions, you might let your adrenaline take over and end up starting a race too fast. Conversely, your legs may feel unexpectedly heavy at the outset, forcing you to drop off your intended pace. But when you find yourself off pace, "You need to correct the mistake as early as possible," says exercise physiologist Jason Karp, Ph.D. Why? So you don't waver too wildly off schedule.

Here's what to do: Gradually adjust your pace. If you've started out too fast, gently slow down. If you've slowed too much, add a smooth surge. (Don't sprint to catch up to your next split time; you'll potentially exhaust yourself for the remainder of the race, Karp says.) On those days when you find yourself unable to sustain the pace you'd hoped for, find a steady gait you can handle and hold on to that for a while, then try to up the pace once you start feeling better.

Go into your event prepared with pacing plans A, B, and C. When Kendal Bradley, 25, races, the Toronto resident wears three pace bands (those bracelets that list split times for a particular finish goal). The first is for the bare minimum time she'd be satisfied with if the weather turns ugly or she feels lousy. The second is for the time she'd be happy with but isn't her PR. The third? Of course. "That's the time I could run," she says, "if conditions are perfect and I'm pushing for a personal best."